Nonclogging marine grille with unpowered weed-cutting provisions

ABSTRACT

A nonclogging marine grille which includes a plurality of rod members extending rearwards from the forward end in cantilevered fashion substantially the full distance across the water inlet opening in the direction of vessel travel and spaced to prevent the passage therebetween of harmful debris and shaped to cause debris to move therealong due to hydrodynamic forces acting thereagainst due to vessel motion. The rod members terminate short of the after end of the inlet and at a selected distance therefrom so that objectionable debris cannot pass through the gap between the rod member ends and the inlet surface but so that weeds which have draped across the rod members and passed aft free of the rod members may be ingested into the inlet or passed free thereof. The grille also includes a central stiffener member similarly shaped but extending across the full inlet opening length and projecting from the hull and outwardly of said rod members to prevent damage to the inlet grille during beaching and shallow water operations, and including weed cutters propelled by weed movement and hydrodynamic forces coacting therewith to cut any weeds which drape therearound and are passed to the after end thereof and which would otherwise clog the inlet.

United States Patent [72] lnventor Niels Alf Svensen Avon, Conn. [21 Appl. Nov 838,820 [22] Filed July 3, 1969 [45] Patented May 25, 1971 [73] Assignee United Aircraft Corporation East Hartford, Conn.

[54] NONCLOGGIN G MARINE GRILLE WITH UNPOWERED WEED-CUTTING PROVISIONS 26 Claims, 14 Drawing Figs.

[52] US. Cl l15/0.5, 60/221 [5 l] Int. Cl B63h 5/16 [50] Field of Search l l5/0.5; 60/221 [5 6] References Cited UNITED STATES PATENTS 3,147,733 9/1964 Engel 115/05 Primary Examiner-Andrew l-l. Farrell Attorney-Vernon F. Hauschild ABSTRACT: A nonclogging marine grille which includes a plurality of rod members extending rearwards from the forward end in cantilevered fashion substantially the full distance across the water inlet opening in the direction of vessel travel and spaced to prevent the passage therebetween of harmful debris and shaped to cause debris to move therealong due to hydrodynamic forces acting thereagainst due to vessel motion. The rod members terminate short of the after end of the inlet and at a selected distance therefrom so that objectionable debris cannot pass through the gap between the rod member ends and the inlet surface but so that weeds which have draped across the rod members and passed aft free of the rod members may be ingested into the inlet or passed free thereof. The grille also includes a central stiffener member similarly shaped but extending across the full inlet opening length and projecting from the hull and outwardly of said rod members to prevent damage to the inlet grille during beaching and shallow water operations, and including weed cutters propelled by weed movement and hydrodynamic forces coacting therewith to cut any weeds which drape therearound and are passed to the after end thereof and which would otherwise clog the inlet.

Patented May 25, 1971 5 Sheets-Sheet 1 N 5 WW WM W l r m m Patented May 25, 1971 3,580,210

3 Sheets-Sheet 2 Patented May 25, 1971 3,580,210

3 Sheets-Sheet 3 FIG- /1;"

NONCLOGGING MARINE GRILLE WITH UNPOWERED WEED-CUTTING PROVISIONS BACKGROUND OF THE. INVENTION 1. Field of Invention This invention relates to grilles which extend across the water inlet ducts located below the waterline in the hull of marine vessels, such as water jet propelled boats, and particularly to such grilles which are nonclogging in nature in that they pass all debris which would be undesirable from an ingestion standpoint clear of the inlet and which pass all ingestible debn's into the inlet in either cut or uncut fashion.

2. Description of the Prior Art In the marine water inlet, debris ingestion and weed clogging presents substantial problems with respect to equipment damage and craft performance degradation, particularly when these water inlets are components integral to duct systems including pumps used for water jet propulsion.

Weed cutters have been utilized, but these cutters have been power driven, such as in U.S. Pat. Nos. 3,046,735 and 3,302,605. Such an arrangement has the disadvantage that special weed cutting drive equipment must be provided with the attendant mechanical complication and added weight penalty thereof. Reciprocating saw action cutters have also been used as in U.S. Pat. No. 3,128,740, but these impose the same added complications and weight penalties to marine craft systems.

Bar members have been provided to extend across water duct inlets but such bars encounter weed-clogging problems and provisions have had to be made in the prior art to either mount the bars pivotally for weed clearing motion as in U.S. Pat. Nos. 3,343,368 and 3,253,567 to clear the weeds from the grille, or grilles are fabricated so that a vibratory action can be imparted 'thereto to prevent weeds from adhering thereto as in U.S. Pat. Nos. 3,253,567 and 3,040,695.

Scissors-type weed cutters have also been provided, such as in U.S. Pat. No. 3,094,965; but all of the aforementioned weed cutting devices require power driving means with its attendant added complication and weight.

Other grilles in the prior art have utilized cantilevered rod members extending across the water duct inlet-but such cantilevered rod members are highly susceptible to damage, due to their unsupported condition, and would not be suitable for a marine craft which would be used in beaching and shallow water operations where grounding and bottom scraping are likely to be encountered. Such grilles are shown in U.S. Pat. Nos. 3,I47,733 and 3,040,695. With respect to the latter, it should be noted that the cantilevered beams extend downstream of the inlet and project outwardly therefrom to create drag and that the central support member does not extend outwardly therebeyond to protect these cantilevered members in a beaching operation or a grounding mishap, or against large debris impingement. Further, in this prior art construction, it will be noted that this central support member is not cantilevered and therefore the elongated weeds which become draped therearound in straddle fashion and are forced aft therealong due to hydrodynamic action will accumulate at the after end thereof and build up so as to clog the inlet and cause flow separation of the water along the duct downstream thereof.

SUMMARY OF INVENTION A primary object of the present invention is to provide an inlet grille for a water duct opening in the hull of a marine vessel, such as a vessel of the jet pump type, which prevents large debris ingestion, which permits limited vegetation ingestion, and which includes provisions for cutting objectionable vegetation.

In accordance with the present invention, the grill is provided with a central stifi'ener which projects beyond the vessels skin a greater distance than the remainder of the grille thereby serving to protect the grille during beaching operation and when struck by large debris.

In accordance with a further aspect of the present invention, the grille includes a plurality of cantilevered rod members which extend substantially the full distance across the water duct inlet and are shaped with respect to the vessels hull to cause weeds and debris to move therealong due to hydrodynamic forces in an aft direction, and are spaced so as to prevent the passage of objectionable debris therebetween and to cause other debris to pass therealong and free of the after end thereof. A limited amount of vegetation can pass between the after end of the cantilevered members and the inlet opening, thereby preventing weed clogging and buildup at the after end of the rod members with its attendant duct clogging and cavitation.

In accordance with still a further aspect of the present invention, the central stiffener member includes a weed-cutting slot at the after end thereof which has knife edges and which coacts with rotary cutters to cut weeds which are draped across the center stiffener and moved aft into the slot, for cutting and eventual ingestion into the water duct and water pump system.

In accordance with a further aspect of this invention, the rotary cutters are shaped so as to be actuated both by hydrodynamic forces acting thereagainst due to the motion of the marine vessel through the water and also by the action of weeds becoming hooked thereto in their passage along the central stiffener member.

In accordance with still a further aspect of the present invention, the rotary cutters include cutting blades which are fabricated to present flexible surfaces to the oncoming debris, thereby serving as a shock absorber to protect the cutter wheel from the full impact effect of debris impingement.

In accordance with a further aspect of the present invention, the grill is readily detachable from the marine vessel hull to permit cleaning and maintenance.

In accordance with still a further aspect of the present invention, the cutting blade of the rotary cutter and .the weed cutting slot of the central stiffener are shaped and positioned so as to coact to impart a shearing action to the weeds in performing the cutting operation.

In accordance with still a further aspect of the invention, each of the cutting blades of the rotary cutter includes a weed hook which is shaped to be positively engaged by the weeds which are migrating aft along the stiffener member so that the hydrodynamic forces acting on the hooked weeds to cause their further migration will, in fact, cause the cutter to rotate. This weed hook performs the further function of causing water which impinges thereagainst during vessel motion through the water to have change of direction in passing therearound so as to impart hydrodynamic forces to the blade and hence rotary motion establishing forces to the rotary cutter.

In accordance with still a further aspect of the present invention, the rotary weed cutters are supported from the central stiffener member and include substantial hub members which insure true alignment and rotation of the rotary cutters with respect to'the cutting surfaces of the central members.

In accordance with still a further aspect of the present invention, each cutting blade is shaped so as to present greater resistance to water flow passing thereover during vesselmotion when the cutter is moving in the direction opposite to the direction of vessel motion, than is imparted thereto when the blade is moving in the direction of vessel motion, thereby establishing rotary motion of the cutters by hydrodynamic forces acting thereagainst.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a modern marine vessel propelled by a jet-pump utilizing my invention.

FIG. 2 is a front view of the marine vessel shown in FIG. 1.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 4.

FIG. 4 is a bottom view of the inlet screen or grille which is the subject matter of my invention.

FIG. 5 is a sketch illustration of the action of sea vegetation in moving along and eventually clogging a portion of the inlet of a water duct, the clogging of which is corrected by my invention.

FIG. 6 is a view taken along line 6-6 of FIG. 7 to show two rotary cutters positioned on the inlet grille central member.

FIG. 7 is a side sectional view of one of the rotary cutters used on my nonclogging inlet grille.

FIG. 8 is a side view of such a rotary cutter mounted with respect to the weed cutting slot of the central stiffener member of the inlet grille or screen to show coaction therebetween.

FIG. 9 is a view taken along line 9-9 of FIG. 7 to show the relative location of the cutting edges of the rotary cutter to those of the central member.

FIG. 10 is a showing of a two-bladed cutter of the contour used for the cutters of my invention to show that they are hydrodynamically propelled.

FIG. 11 is a view taken along line 1141 of FIG. 10.

. FIG. 12 is a view taken along line 12-12 of FIG. 10.

FIGS. 13 and 14 correspond to FIGS. 11 and 12, respectively, but illustrate a different cutter contour.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 we see the hull 14 of a marine vessel 10 of the jet pump-propelled type utilizing my invention. Hull 10 includes bow 16, transom stem 18, and port and starboard sideboards 28 and 22, respectively. Keel 241 extends longitudinally along the centerline of the bottom of the hull 10 from the bow 16' to the transom stem 18.

Vessel 10 is propelled through the water by jet-pump unit 26 which, as best shown in FIG. 1, includes water duct 28 having an inlet or suction side 30 positioned in and extending through the bottom or skin 32 of hull l4 and having an exit nozzle or outlet end 36. Water pump 38, which is driven by motor through appropriate and conventional shafting 42, is positioned in water duct 28 and performs the function of drawing water into duct 28 through inlet 30, adding pressure and velocity thereto in passing therethrough and then discharging the pumped water through outlet nozzle 34 to furnish propulsive thrust to drive the vessel 10 through the water.

Experience has shown that pump blading 38 must be protected from debris and excessive amounts of water vegetation when operating in bodies of water which contain same; and, accordingly, it is desirable to place an inlet grille across inlet 30 so as to prevent the ingestion of objectionable debris and excessive amounts of vegetation thereby eliminating the possibility of pump damage and clogging.

As best shown in FIG. 2, for vessels which have sufficient propulsion power requirements, twin propulsor systems, such as 26, are positioned on opposite sides of vessel centerline 12 and water is pumped thereinto through inlet grilles 50.

As previously stated, it is highly desirable that grille 50 be fabricated so that debris of a size which could damage or clog pump 38 be restrained from entering duct 28 and that vegetation entry therethrough be controlled for the same reasons.

Jet-pump system 26 will not be described in greater particularity since many systems would suffice for use with my inlet grille, and reference may be had to US. Pat. No. 3,387,583 for a more particular description of one such system.

By considering FIGS. 3 and 4 we will now consider the construction of inlet grill 50 in greater particularity. Water duct 28 is connected in any convenient fashion to flange member or frame 52, which in turn is connected to vessel bottom 32 by any convenient means, such as bolted flange member 54. Frame 52 may be contoured as shown in FIG. 3 to cooperate with duct 28 in defining a smooth, substantially regular surface duct inlet 30. As best shown in FIG. 4, frame 52 is of elliptical or oval shaped cross sectionincluding a longitudinal axis 56; the shape of frame 52 will, however, depend on inlet configuration. Central stiffening member 59 extends along longitudinal axis 56 of inlet screen 50 and frame 52 and is connected at its forward end 60 and at its after end 62 to frame 52 so as to be supported rigidly therefrom. The inner surface 64 of stiffener extends across frame 5'2 and its outer surface 66 projects a substantial distance therefrom and outwardly beyond skin or hull bottom 32 to perform the function of protecting cantilevered grill or rod members 68, 70, 72, 74, 76, and 78. These rod members 68-78 are attached to the forward end 82 of frame 52 at their forward ends and project in spaced relation parallel to central stiffener 59 toward the after end of frame 52. Central stiffener 59 and grille members 68-78 are connected at their forward ends to the forward end 82 of frame 52 by any convenient method, such as welding or bolting. The forward and after ends, 60 and 62, of central stiffener 59 may be similarly attached to the forward and after ends, 82 and 88, of frame 52. Grille rod members 68-78 are shaped as best shown in FIG. 3 to have arcuate top and bottom surfaces 84 and 86 which converge from the forward end 98 to the after end 92 thereof. Thus it may readily be seen that cantilevered grille members 6878 are actually cantilevered, single leaf, tapered springs which can accommodate dynamic impacts from floating debris.

It will be noted that grille or rod members 68-78 extend parallel to central stiffener 59 and are spaced with respect thereto and with respect to each other so that objectionable debris which would be capable of clogging or damaging pump 38 cannot pass therebetween.

Usually the grille axis 56 and grille rod members 59 and 68- -78 extend parallel to craft centerline; but, under certain cir cumstances it may prove advantageous to place these members in better alignment with the hydrodynamic flow of water underneath the skin 32, if this flow is different from a direction parallel to centerline.

It will also be noted that the outer surface 66 of stiffener 59 and the outer surfaces, such as 86 of grille members 68-78 are canted or project outwardly from bottom 32 so that debris which impinges against the grille at the forward end thereof is caused to move outwardly along surfaces 66 and 86 in an after direction due to the hydrodynamic force of water passing thereover caused by vessel motion and will eventually pass clear of water duct inlet 30 due to this fend-off action of grille 50 and will pass aft of grille 50 along bottom skin 32, having been prevented from entering inlet 30. This is particularly true of all large size debris, such as floating logs and lumber, and branches, and will be true for much of the vegetation and weed variety of debris which will be encountered.

As best illustrated in FIG. 5, some elongated weeds such as W will drape around or straddle either stiffener 59 or grille members 68-78 and be caused to migrate or pass therealong from a forward to an after direction due to hydrodynamic water forces acting thereon and will eventually lodge and build up as shown at station W at the after end 62 of central stiffener 59, thereby not only partially blocking waterflow into inlet 30 but also establishing a flow separation region F upstream thereof along the inner wall of duct 28 so as to effectively restrict inlet water flow area to area A.

This weed accumulation or buildup is therefore highly objectionable and to prevent such buildup cantilevered members 68-78 are terminated just short of the after surface 96 of inlet 30 to thereby free the weeds for passage aft of inlet 30 or for ingestion through aperture 98, fonned between the downstream ends, such as 108 of cantilevered members 68- 78 and the after surface 96 of inlet 30.

In view of the fact that center stiffener 59 need be secured to frame 52 at both its forward end 60 and its after end 62 for strength purposes, it cannot be cantilevered and therefore the weed accumulation shown at W in FIG. 5 will occur therealong. It is accordingly an important teaching of this invention that stiffener 59 be contoured to define weed cutting slot 102 and is provided with rotary cutters, best shown in FIGS. 6-9, on opposite sides thereof for coaction therewith in cutting the draped weeds so accumulated.

As best shown in FIGS. 6-9, rotary cutters 110 and 112 are positioned on opposite sides of stiffener 59 and supported therefrom for rotation adjacent to weed-cutting slot 102 which includes knife edges along surfaces 114 and 116 on stiffener 59, and cutter cutting edges. Rotary cutters 110 and 112 are positioned on hubs 122 and 124, which envelop shaft or bolt member 126 passing through the central bore thereof and through aperture 128 of stiffener 59 and are held snugly in position thereon by bolt head 130 and nut 132 so as to cause cutters 110 and 112 to rotate true and to avoid any type of wobbling or wiggling motion which would bring their cutting surfaces (to be described hereinafter), out of cutting engagement with the cutting surfaces of weed cutting slot 102. A single cutter, such as 110, is shown in FIG. 7 and includes four equally spaced cutting blades 140, 142, 144, and 146 projecting from hub 124 thereof for rotation about axis 148. The cutting blades 140-146 include leading edge cutting edges 150-156 and selectively contoured trailing edge surfaces 160-166 which are fabricated of an impact compliant material, such as rubber, so as to serve as a shock absorber when heavy or fast-traveling debris impinges thereagainst during vessel operation to partially absorb the shock and force of the debris impingement and thereby preserve the mechanical integrity of cutters 110 and 112.

As best shown in FIG. 9, the corresponding cutting arms 146 and 146' of cutting wheels 110 and 112 are shaped to be substantially triangular in cross section and to have a first surface 170 and 170' which extend parallel to the cutting edge surfaces of stiffener 59, second rear surfaces or legs 172 and 172, which extend substantially perpendicular to the cutting edge surfaces of stiffener 59 and the triangle hypotenuse surfaces 174 and 174 which extend between the tips of and cooperate with sides 170 and 170' to define cutting edges 156 and 156'.

As best shown in FIG. 8, wheels 110 and 112 are positioned to rotate about axis 148, which is offset with respect to weedcutting slot 102 so that the cutting edges, such as 156, will form an angular interface with the cutting surface 114 of weed-cutting slot 102, defining angle a therebetween, so as to form a shearing type out upon the weeds lodged in slot 102. It will be noted that weed cutters 110 and 112 are not mechanically powered but, in a fashion to be described hereinafter, are powered but, in a fashion to be described hereinafter, are powered hydrodynamically either by water passing thereacross or water acting on weeds lodged thereon.

With respect to the weed propulsion mode of operation, it will be noted that each of cutting blades 140-146 includes a weed hook such as 200 which serves to hook weeds being carried by the water due to forward vessel motion from the forward end 82 to the after end 80 of grille 50 so that the combined effect of the water passing pump inlet 30 along skin 32 and the suction effect acting on such water by pump 38 will impose hydrodynamic forces on the weeds so hooked and those forces will act to cause rotary cutters 110 and 112 to rotate about axis 148 to perform their weed cutting functions. Hook 200 of each blade directs the weeds hooked thereon into slot 102 for cutting by the next succeeding blade.

Cutting members 110 and 112 may be independently mounted on the bolt support system 126-132 or may be mounted by use appropriately sized shear pins 202 and 204 through hubs 122-124 so that the four blades of cutter 110 are rotationally staggered approximately 45 with respect to the four blades of cutter 112 so that the weeds lodged in slot 102 at any given time have a single cut performed thereon.

Now considering FIGS. -13, we shall see how cutters 110 and 112 are contoured so that the hydrodynamic force caused by water passing therearound and thereacross due to vessel motion will propel the cutters in rotary motion. FIG. 10 is a representation of a two-bladed cutter 110 rotating about axis 148 and including blades 142' and 146' extending therefrom and including leading cutting edge surfaces 156 and 152 and trailing, shock absorbing, and weed catching surfaces 166 and 162'. Vessel 10 is moving in the direction of arrow A and therefore the apparent relative motion of the water passing along the hull of the vessel and across cutter is in direction B and will cause the cutter to rotate in a counterclockwise direction about axis 148 in view of the cutter contouring, now to be described.

FIG. 11, which is the section taken along line 1l-11 of FIG. 10 and shows blades 146 and 146" of rotating cutters 110' and 112', respectively, positioned on opposite sides of stiffener member 59'. It will be noted that cutter blades 146 and 146" present substantially large area and substantially perpendicular surfaces 166' and 166" to the water travelling with respect to the cutters in direction B in attempting to pass over or around cutter blades 146' and 146". The momentum force of the water acting against these surfaces and the directional change imparted to the water flowing around these surfaces combine to cause cutter blades 146 and 146" to rotate in a counterclockwise direction FIGS. 7 and 8). The force illustrated in the FIG. 11 construction as tending to move the blades in a counterclockwise direction, is equal to the area of surfaces 166 and 166" times the force of the water acting against those areas.

Viewing FIG. 12, which is the section taken along line 12-12 of FIG. 10, we see blades 142 and 142" of cutters 110 and 112' positioned on opposite sides of stiffener 59'. These blades include leading or cutting edge 152' and 152", surfaces 250 and 252 extending along stiffener 59', surfaces 254 and 256 projecting perpendicular to stiffener 59' and acute, diverging surfaces 258 and 260, forming an acute angle with and diverting slightly from a plane parallel to stiffener 59'. It will be noted by viewing FIG. 12 that the water passing over blades 142 and 142" need merely make a slight directional change over surfaces 258 and 260 and the only forces imparted to blades 142 and 142" by this water motion is the sum of the surface resistance force along surfaces 258 and 260, the slight directional change force, and the eddy force caused by the water passing in eddy fashion back along surfaces 254 and 256. It can be shown mathematically that this resistive force tending to move blades 142' and 142" in a clockwise direction is substantially less than the force tending to move blades 146' and 146" in a counterclockwise direction, therefore cutting wheels 110' and 112 will rotate in a counterclockwise direction due to the hydrodynamic forces of the water acting thereagainst in passing therearound. In this connection, there is one added function performed by weed hook 200 (see FIG. 8) in that the directional change imparted to the water impinging thereagainst will be an added force to the FIG. 11 arrangement tending to cause cutter rotation in the counterclockwise direction.

To take further advantage of the hydrodynamic forces acting against the blade, the blades could be contoured as shown in FIGS. 13 and 14, which correspond to FIGS. 11 and 12 previously described. Cutting blades 300 and 302 include concave surfaces 304 and 306, which cause a greater change in the direction of flow of the water passing therearound to increase the total force which imparts a counterrotating force to the cutter blades. Blades 308 and 310 are substantially diametrically opposed to blades 300 and 302 and include concave surfaces 312 and 314 to provide an even smoother directional flow to the water passing thereover to decrease the total force imparting a clockwise rotational force to blades 308 and 310 and hence cutters corresponding to 110 and l 12,

lclaim:

1. A weed-cutting grille adapted to be connected to a water inlet in the hull of a marine vessel and including:

a. a frame member adapted to be connected to the vessel skin at the inlet,

b. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including:

l. a weed-cutting slot at the after end thereof having:

A. at least one cutting edge,

c. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including:

1. a cutting surface adjacent the stiffener member and positioned to pass immediately adjacent and in cutting relation to said cutting edge of weed cutting slot during weed cutter rotation and,

2. each blade being shaped to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.

2. Apparatus according to claim 1 wherein each of said cutting blades is shaped to present maximum resistance to water passage thereby when the blade is traveling in the direction opposite to vessel motion, and minimum resistance to water passage thereby when the blade is traveling in the direction of vessel motion so that said rotary cutter is caused to rotate by the hydrodynamic forces acting thereagainst.

3. Apparatus according to claim 2 and wherein said stiffener member includes two cutting surfaces and further including a second rotary cutter positioned on the opposite side of the stiffener member from the first rotary cutter and cooperating with the stiffener member to cut weeds located in said weedcutting slot.

4. Apparatus according to claim 3 and including means to connect and disconnect said frame member to the hull.

5. Apparatus according to claim 3 wherein each of said cutting blades is of substantially triangular cross section wherein one of the legs of the triangle extends along and parallel to the cutting edge of the stiffener member, one of the legs of the triangle projects substantially perpendicular to the cutting edge of the stiffener member and is adapted to present maximum resistance to the passage of water thereby and thereacross as the cutting blade moves in a direction opposite to vessel travel, and wherein the hypotenuse cooperates with the first leg in defining the cutting edge of the blade at the intersection therebetween and presents a smooth, acute angle surface for the water to pass over when the cutter is traveling in the direction of vessel travel so that the rotary cutter is caused to rotate by hydrodynamic forces acting thereagainst.

6. Apparatus according to claim 5 wherein said second leg is of concave construction and wherein said hypotenuse is of concave construction.

7. Apparatus according to claim 1 wherein each of said cutting blades is of substantially triangular cross section wherein one of the legs of the triangle extends along and parallel to the cutting edge of the stiffener member, one of the legs of the triangle projects substantially perpendicular to the cutting edge of the stiffener member and is adapted to present maximum resistance to the passage of water thereby and thereacross as the cutting blade moves in a direction opposite to vessel travel, and wherein the hypotenuse cooperates with the first leg in defining the cutting edge of the blade at the intersection therebetween and presents a smooth, acute angle surface for the water to pass over when the cutter is traveling in the direction of vessel travel so that the rotary cutter is caused to rotate by hydrodynamic forces acting thereagainst.

8. Apparatus according to claim 2 wherein each of said cutting blades is of substantially triangular cross section wherein one of the legs of the triangle extends along and parallel to the cutting edge of the stiffener member, one of the legs of the triangle projects substantially perpendicular to the cutting edge of the stiffener member and is adapted to present maximum resistance to the passage of water thereby and thereacross as the cutting blade moves in a direction opposite to vessel travel, and wherein the hypotenuse cooperates with the first leg in defining the cutting edge of the blade at the intersection therebetween and presents a smooth, acute angle surface for the water to pass over when the cutter is traveling in the direction of vessel travel so that the rotary cutter is caused to rotate by hydrodynamic forces acting thereagainst.

9. A weed-cutting grille adapted to be connected to a water inlet in the hull ofa marine vessel and including:

a. a frame member adapted to be connected to the vessel skin at the inlet,

b. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and in- A cluding:

'l at least one cutting surface,

c. a rotary cutterT'mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including:

l. a cutting surface adjacent the cutting surface of the stiffener rnember and positioned to pass immediately adjacent and in cutting relation thereto during weed cutter rotation and,

2. each blade being shaped and positioned to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.

10. A weed-cutting grille adapted to be connected to a water inlet in the hull of a marine vessel and including:

a. a frame member adapted to be connected to the vessel skin at the inlet,

b. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including: 1 at least one cutting surface,

c. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including:

1. a cutting surface adjacent the cutting surface of the stiffener member and positioned to pass immediately adjacent and in cutting relation thereto during weed cutter rotation and,

2. each of said cutting blades being shaped to present maximum resistance to water passage thereby when the blade is traveling in the direction opposite to vessel motion and minimum resistance to water passage thereby when the blade is traveling in the direction of vessel motion so that said rotary cutter is caused to rotate by the hydrodynamic forces acting thereagainst.

11. A marine vessel having a hull and a keel-type projection on the hull longitudinal centerline, and also having two weedcutting grilles each adapted to be connected to a water inlet in the hull of the marine vessel on opposite sides of the keel-type projection and including:

a. a frame member adapted to be connected to the vessel skin at the inlet,

b. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and projecting from the hull to be in substantial horizontal alignment with said keel-type projection to coact therewith in leveling the vessel during grounding operation including: l. at least one cutting surface,

c. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including:

1. a cutting surface adjacent the cutting surface of the stiffener member and positioned to pass immediately adjacent and in cutting relation thereto during weed cutter rotation and,

2. blade being shaped and positioned to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.

12. A marine vessel having a hull and a keel-type projection on the hull longitudinal centerline, and also having two weedcutting grilles adapted to be connected to a water inlet in the hull of the marine vessel on opposite sides of the keel-type projection and including:

a. a frame member adapted to be connected to the vessel skin at the inlet,

b. at least one stiffener m amber supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and projecting from the hull to be in substantial horizontal alignment with said keel-type projection to coact therewith in leveling the vessel during grounding operation including:

1. at least one cutting surface,

c. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including:

1. a cutting surface adjacent the cutting surface of the stiffener member and positioned to pass immediately adjacent and in cutting relation thereto during weed cutter rotation and,

2. each of said cutting blades being shaped to present maximum resistance to water passage thereby when the blade is traveling in the directionopposite to vessel motion and minimum resistance to water passage thereby when the blade is traveling in the direction of vessel motion so that said rotary cutter is caused to rotate by the hydrodynamic forces acting thereagainst.

13. Apparatus according to claim 9 wherein each of said cutting blades is shaped to present maximum resistance to water passage thereby when the blade is traveling in the direction opposite to vessel motion and minimum resistance to water passage thereby when the blade is traveling in the direction of vessel motion so that said rotary cutter is caused to rotate by the hydrodynamic forces acting thereagainst.

14. A weed-cutting grille adapted to be located at the inlet of a water duct in the skin of a marine vessel and including:

a. grille support means adapted to be connected to the vessels skin at the water duct inlet,

a rigid member supported from and extending across the support member in the direction of vessel travel and shaped to project from the vessels skin and to define a weed-cutting slot at the after end thereof so that weeds which drape across said rigid member will be carried from the forward to the after end of the rigid member during vessel travel and eventually be lodged in said weed cutting slot, having:

1. cutting edges on opposite sides thereof at the weedcutting slot,

c. a rotary cutter positioned on each side of said rigid member and each having a plurality of cutting blades extending therefrom and each cutting blade:

1. having a cutting edge located adjacent the cutting edge of the rigid member weed-cutting slot and positioned to pass adjacent to and across said weed-cutting slot during cutter rotation so as to cooperate with said rigid member cutting edge in cutting any weeds located in said slot and,

2. shaped to present maximum resistance to water passage therearound when rotating in a direction opposite to vessel motion and minimum resistance to water passage therearound when rotating in the direction of vessel motion so that the cutter will be caused to rotate by hydrodynamic forces acting thereagainst.

15. Apparatus according to claim 14 and wherein each blade of said weed cutter is shaped todefme a weed hook opening in the direction of vessel travel when the blade is traveling in a direction opposite to vessel travel to thereby intercept the weeds which are passing along the rigid member so that the added resistance to water passage thereby caused by the hooked weed will add to the total hydrodynamic force tending to cause the rotary cutters to rotate,

16. Apparatus according to claim 15 wherein each of said rotary cutters has a hub member at the inner diameter thereof mounted for rotation about an axle member extending through and supported by an aperture in said rigid member so that said rotary cutters will rotate squarely with respect to said rigid member.

17. Apparatus according to claim 16 and including grille means located on opposite sides of said rigid member and extending across the remainder of the inlet to prevent large objects from entering the inlet.

18. Apparatus according to claim 17 wherein said grille members include a plurality of rod members connected to and supported by the forward end of the support means and extending therefrom in cantilevered fashion in a direction parallel to said rigid member and terminating short of the downstream and of the support means and spaced with respect to adjacent rod members and said rigid member so that large objects cannot pass therebetween and so that any weed which drapes across any of said rod members and is caused to move from the forward end to the after end thereof by hydrodynamic forces acting thereon will be freed at the after end thereof to enter said inlet.

19. Apparatus according to claim 14 wherein each of said rotary cutters has four equally spaced cutting blades and wherein said-cutters are mounted for independent rotation.

20. Apparatus according to claim 14 wherein each of said rotary cutters includes four equally spaced blades and wherein said cutters are mounted for rotation together with the blades of the first cutter substantially bisecting the angular spacing between the blades of the second cutter so that the cutters perform their cutting operations independently.

21. A marine vessel including a hull having a bow, a stern, and a bottom skin and having:

a. a water duct having an inlet in the bottom skin of the hull and an outlet at the stern so that water may pass through said duct from said inlet'in the bottom skin and to be discharged through said outlet in the stern to propel the vessel,

b. a water-pumping unit positioned in said duct to pump water therethrough,

c. a weed-cutting grille located at the water duct inlet and having:

I. a frame member adapted to be connected to the vessel skin at the inlet,

2. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including:

A. at least one cutting surface,

3. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including:

A. a cutting surface adjacent the cutting surface of the stiffener member and positioned to pass immediately adjacent and in cutting relation thereto during weed cutter rotation and,

B. each of said cutting blades being shaped to present maximum resistance to water passage thereby when the blade is traveling in the direction opposite to vessel motion and minimum resistance to water passage thereby when the blade is traveling in the direction of vessel motion so that said rotary cutter is caused to rotate by the hydrodynamic forces acting thereagainst.

22. A marine vessel including a hull having a bow, a stern, and a bottom skin and having:

a. a water duct having an inlet in the bottom skin of the hull and an outlet at the stern so that water may pass through said duct from said inlet in the bottom skin and to be discharged through said outlet in the stern to propel the vessel,

b. a water-pumping unit positioned in said duct to pump water therethrough,

c. a weed-cutting grille located at the water duct inlet and having:

I. a frame member adapted to be connected to the vessel skin at the inlet,

2. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including:

A. at least one cutting surface,

3. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including:

A. a cutting surface adjacent the cutting surface of the stiffener member and positioned to pass immediately adjacent and in cutting relation thereto during weed cutter rotation and,

B. each blade being shaped and positioned to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.

23. A marine vessel including a hull having a bow, a stern,

and a bottom skin and having:

a. a water duct having an inlet in the bottom skin of the hull and an outlet at the stern so that water may pass through said duct from said inlet in the bottom skin and to be discharged through said outlet in the stem to propel the vessel,

b. a water-pumping unit positioned in said duct to pump water therethrough,

c. a weed-cutting grille located at the water duct inlet and having:

' l. a frame member adapted to be connected to the vessel skin at the inlet,

2. a least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including:

A. a weed-cutting slot at the after end thereof having:

I. at least one cutting edge,

3. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including:

A. a cutting surface adjacent the stiffener member and positioned to pass immediately adjacent and in cutting relation to said cutting edge of weed-cutting slot during weed cutter rotation and,

B. each blade being shaped to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.

24. Apparatus according to claim 1 and wherein said rotary cutter is positioned in offset relation to said stiffener member and wherein said weed-cutting slot has a flat base which constitutes part of its cutting surface and wherein said cutting blades are shaped so that said cutting surface of the cutting blades define an angular interface with said cutting surface of said weed cutting slot base so that said cutting surfaces perform a shearing action on weeds lodged in said weed-cutting slot.

25. Apparatus according to claim 15 wherein said weed hook is fabricated of resilient material so that it serves as a shock absorber for the cutter when solid objects impinge thereagainst.

26. Apparatus according to claim 15 wherein said weed hook is shaped to substantially reverse the flow of water attempting to pass therearound due to vessel motion to add further to the total by hydrodynamic force tending to cause the rotary cutters to rotate. 

1. A weed-cutting grille adapted to be connected to a water inlet in the hull of a marine vessel and including: a. a frame member adapted to be connected to the vessel skin at the inlet, b. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including:
 1. a weed-cutting slot at the after end thereof having: A. at least one cutting edge, c. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including:
 1. a cutting surface adjacent the stiffener member and positioned to pass immediately adjacent and in cutting relation to said cutting edge of weed cutting slot during weed cutter rotation and,
 2. each blade being shaped to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.
 2. each blade being shaped to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.
 2. Apparatus according to claim 1 wherein each of said cutting blades is shaped to present maximum resistance to water passage thereby when the blade is traveling in the direction opposite to vessel motion, and minimum resistance to water passage thereby when the blade is traveling in the direction of vessel motion so that said rotary cutter is caused to rotate by the hydrodynamic forces acting thereagainst.
 2. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including: A. at least one cutting surface,
 2. a least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including: A. a weed-cutting slot at the after end thereof having: I. at least one cutting edge,
 2. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including: A. at least one cutting surface,
 2. shaped to present maximum resistance to water passage therearound when rotating in a direction opposite to vessel motion and minimum resistance to water passage therearound when rotating in the direction of vessel motion so that the cutter will be caused to rotate by hydrodynamic forces acting thereagainst.
 2. each of said cutting blades being shaped to present maximum resistance to water passage thereby when the blade is traveling in the direction opposite to vessel motion and minimum resistance to water passage thereby when the blade is traveling in the direction of vessel motion so that said rotary cutter is caused to rotate by the hydrodynamic forces acting thereagainst.
 2. blade being shaped and positioned to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.
 2. each of said cutting blades being shaped to present maximum resistance to water passage thereby when the blade is traveling in the direction opposite to vessel motion and minimum resistance to water passage thereby when the blade is traveling in the direction of vessel motion so that said rotary cutter is caused to rotate by the hydrodynamic forces acting thereagainst.
 2. each blade being shaped and positioned to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.
 3. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including: A. a cutting surface adjacent the stiffener member and positioned to pass immediately adjacent and in cutting relation to said cutting edge of weed-cutting slot during weed cutter rotation and, B. each blade being shaped to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.
 3. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including: A. a cutting surface adjacent the cutting surface of the stiffener member and positioned to pass immediately adjacent and in cutting relation thereto during weed cutter rotation and, B. each of said cutting blades being shaped to present maximum resistance to water passage thereby when the blade is traveling in the direction opposite to vessel motion and minimum resistance to water passage thereby when the blade is traveling in the direction of vessel motion so that said rotary cutter is caused to rotate by the hydrodynamic forces acting thereagainst.
 3. a rotary cutter mounted adjacent said stiffener and including a plurality of cutting blades extending therefrom and each blade including: A. a cutting surface adjacent the cutting surface of the stiffener member and positioned to pass immediately adjacent and in cutting relation thereto during weed cutter rotation and, B. each blade being shaped and positioned to intercept weeds passing from the forward part to the after part of said stiffener member and be propelled in rotary motion thereby.
 3. Apparatus according to claim 2 and wherein said stiffener member includes two cutting surfaces and further including a second rotary cutter positioned on the opposite side of the stiffener member from the first rotary cutter and cooperating with the stiffener member to cut weeds located in said weed-cutting slot.
 4. Apparatus according to claim 3 and including means to connect and disconnect said frame member to the hull.
 5. Apparatus according to claim 3 wherein each of said cutting blades is of substantially triangular cross section wherein one of the legs oF the triangle extends along and parallel to the cutting edge of the stiffener member, one of the legs of the triangle projects substantially perpendicular to the cutting edge of the stiffener member and is adapted to present maximum resistance to the passage of water thereby and thereacross as the cutting blade moves in a direction opposite to vessel travel, and wherein the hypotenuse cooperates with the first leg in defining the cutting edge of the blade at the intersection therebetween and presents a smooth, acute angle surface for the water to pass over when the cutter is traveling in the direction of vessel travel so that the rotary cutter is caused to rotate by hydrodynamic forces acting thereagainst.
 6. Apparatus according to claim 5 wherein said second leg is of concave construction and wherein said hypotenuse is of concave construction.
 7. Apparatus according to claim 1 wherein each of said cutting blades is of substantially triangular cross section wherein one of the legs of the triangle extends along and parallel to the cutting edge of the stiffener member, one of the legs of the triangle projects substantially perpendicular to the cutting edge of the stiffener member and is adapted to present maximum resistance to the passage of water thereby and thereacross as the cutting blade moves in a direction opposite to vessel travel, and wherein the hypotenuse cooperates with the first leg in defining the cutting edge of the blade at the intersection therebetween and presents a smooth, acute angle surface for the water to pass over when the cutter is traveling in the direction of vessel travel so that the rotary cutter is caused to rotate by hydrodynamic forces acting thereagainst.
 8. Apparatus according to claim 2 wherein each of said cutting blades is of substantially triangular cross section wherein one of the legs of the triangle extends along and parallel to the cutting edge of the stiffener member, one of the legs of the triangle projects substantially perpendicular to the cutting edge of the stiffener member and is adapted to present maximum resistance to the passage of water thereby and thereacross as the cutting blade moves in a direction opposite to vessel travel, and wherein the hypotenuse cooperates with the first leg in defining the cutting edge of the blade at the intersection therebetween and presents a smooth, acute angle surface for the water to pass over when the cutter is traveling in the direction of vessel travel so that the rotary cutter is caused to rotate by hydrodynamic forces acting thereagainst.
 9. A weed-cutting grille adapted to be connected to a water inlet in the hull of a marine vessel and including: a. a frame member adapted to be connected to the vessel skin at the inlet, b. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including:
 10. A weed-cutting grille adapted to be connected to a water inlet in the hull of a marine vessel and including: a. a frame member adapted to be connected to the vessel skin at the inlet, b. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and including:
 11. A marine vessel having a hull and a keel-type projection on the hull longitudinal centerline, and also having two weed-cutting grilles each adapted to be connected to a water inlet in the hull of the marine vessel on opposite sides of the keel-type projection and including: a. a frame member adapted to be connected to the vessel skin at the inlet, b. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and projecting from the hull to be in substantial horizontal alignment with said keel-type projection to coact therewith in leveling the vessel during grounding operation including:
 12. A marine vessel having a hull and a keel-type projection on the hull longitudinal centerline, and also having two weed-cutting grilles adapted to be connected to a water inlet in the hull of the marine vessel on opposite sides of the keel-type projection and including: a. a frame member adapted to be connected to the vessel skin at the inlet, b. at least one stiffener member supported from said frame member and shaped and positioned to extend across the inlet in substantially the direction of vessel travel and projecting from the hull to be in substantial horizontal alignment with said keel-type projection to coact therewith in leveling the vessel during grounding operation including:
 13. Apparatus according to claim 9 wherein each of said cutting blades is shaped to present maximum resistance to water passage thereby when the blade is traveling in the direction opposite to vessel motion and minimum resistance to water passage thereby when the blade is traveling in the direction of vessel motion so that said rotary cutter is caused to rotate by the hydrodynamic forces acting thereagainst.
 14. A weed-cutting grille adapted to be located at the inlet of a water duct in the skin of a marine vessel and including: a. grille support means adapted to be connected to the vessel''s skin at the water duct inlet, B. a rigid member supported from and extending across the support member in the direction of vessel travel and shaped to project from the vessel''s skin and to define a weed-cutting slot at the after end thereof so that weeds which drape across said rigid member will be carried from the forward to the after end of the rigid member during vessel travel and eventually be lodged in said weed cutting slot, having:
 15. Apparatus according to claim 14 and wherein each blade of said weed cutter is shaped to define a weed hook opening in the direction of vessel travel when the blade is traveling in a direction opposite to vessel travel to thereby intercept the weeds which are passing along the rigid member so that the added resistance to water passage thereby caused by the hooked weed will add to the total hydrodynamic force tending to cause the rotary cutters to rotate.
 16. Apparatus according to claim 15 wherein each of said rotary cutters has a hub member at the inner diameter thereof mounted for rotation about an axle member extending through and supported by an aperture in said rigid member so that said rotary cutters will rotate squarely with respect to said rigid member.
 17. Apparatus according to claim 16 and including grille means located on opposite sides of said rigid member and extending across the remainder of the inlet to prevent large objects from entering the inlet.
 18. Apparatus according to claim 17 wherein said grille members include a plurality of rod members connected to and supported by the forward end of the support means and extending therefrom in cantilevered fashion in a direction parallel to said rigid member and terminating short of the downstream and of the support means and spaced with respect to adjacent rod members and said rigid member so that large objects cannot pass therebetween and so that any weed which drapes across any of said rod members and is caused to move from the forward end to the after end thereof by hydrodynamic forces acting thereon will be freed at the after end thereof to enter said inlet.
 19. Apparatus according to claim 14 wherein each of said rotary cutters has four equally spaced cutting blades and wherein said cutters are mounted for independent rotation.
 20. Apparatus according to claim 14 wherein each of said rotary cutters includes four equally spaced blades and wherein said cutters are mounted for rotation together with the blades of the first cutter substantially bisecting the angular spacing between the blades of the second cutter so that the cutters perform their cutting operations independently.
 21. A marine vessel including a hull having a bow, a stern, and a bottom skin and having: a. a water duct having an inlet in the bottom skin of the hull and an outlet at the stern so that water may pass through said duct from said inlet in the bottom skin and to be discharged through said outlet in the stern to propel the vessel, b. a water-pumping unit positioned in said duct to pump water therethrough, c. a weed-cutting grille located at the water duct inlet and having:
 22. A marine vessel including a hull having a bow, a stern, and a bottom skin and having: a. a water duct having an inlet in the bottom skin of the hull and an outlet at the stern so that water may pass through said duct from said inlet in the bottom skin and to be discharged through said outlet in the stern to propel the vessel, b. a water-pumping unit positioned in said duct to pump water therethrough, c. a weed-cutting grille located at the water duct inlet and having:
 23. A marine vessel including a hull having a bow, a stern, and a bottom skin and having: a. a water duct having an inlet in the bottom skin of the hull and an outlet at the stern so that water may pass through said duct from said inlet in the bottom skin and to be discharged through said outlet in the stern to propel the vessel, b. a water-pumping unit positioned in said duct to pump water therethrough, c. a weed-cutting grille located at the water duct inlet and having:
 24. Apparatus according to claim 1 and wherein said rotary cutter is positioned in offset relation to said stiffener member and wherein said weed-cutting slot has a flat base which constitutes part of its cutting surface and wherein said cutting blades are shaped so that said cutting surface of the cutting blades define an angulaR interface with said cutting surface of said weed cutting slot base so that said cutting surfaces perform a shearing action on weeds lodged in said weed-cutting slot.
 25. Apparatus according to claim 15 wherein said weed hook is fabricated of resilient material so that it serves as a shock absorber for the cutter when solid objects impinge thereagainst.
 26. Apparatus according to claim 15 wherein said weed hook is shaped to substantially reverse the flow of water attempting to pass therearound due to vessel motion to add further to the total by hydrodynamic force tending to cause the rotary cutters to rotate. 